[7.02] The Boron Abundance of the Hyades Giants

Spectra of two of the Hyades giants $\epsilon$ Tau (HD~28305)
and $\delta^1$ Tau (HD~27697) and the K0II giant $\beta$ Gem (HD~62509) have been obtained with the G270M grating of the GHRS spectrograph of
the Hubble Space Telescope
. A Hyades main sequence F star near the
turnoff was also observed. Boron abundances were determined from spectrum
synthesis of the region near 2500\AA. Since B is destroyed
by (p,$\alpha$) reactions at a temperature near 5 million degrees, its
abundance probes deep internal mixing, mass loss, and depth of the convection
zone of a giant star.
We find that the B abundance in each giant is greatly reduced below solar.
In order to more confidently determine an abundance and not just an upper limit,
we carefully reanalyzed previous HST observations of F stars and also the Solar
Maximum Mission solar spectrum, to identify the amount of line strength due to
possible blending in the region of the B lines. Our final B abundance will
be combined with previous abundance determinations of Li and Be to test models of the convection zone depth in giants, mass loss, and other predictions of
stellar evolution models.